It's no secret that dimming the display on your smartphone, laptop, or tablet is going to prolong the battery life. To figure out how much of a difference it really makes, Wired did the math to see just how much battery life you can squeeze out of an iPhone 4 by dropping the brightness.

We've mentioned before that turning down the brightness extends battery life, but just how much has always been a bit of a mystery. Obviously every phone is a little different, but after doing the math for an iPhone 4, Wired's results show just how important brightness is:

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From this, an iPhone 4 should last about 6.5 hours of continuous use on the lowest brightness setting and about 3.5 hours on the highest brightness setting. That's a pretty big difference. It seems putting the brightness at about half would give a fairly reasonable time of around 5 hours. Remember though, this is with wifi and 3G off. So, really your phone wouldn't even last that long. I think it is safe to say that you will still get more battery time from your phone at half brightness than at full.

How much of a difference in battery life you see also depends on your usage. If you're a power user, lowering the brightness setting can get you a good two hours of extra battery life, but if you don't use your phone that much you won't really see a big difference. If you don't feel like futzing about with your phone's brightness settings, you can automate the process on Android with Tasker, or on a jailbroken iPhone with SBSettings. An even easier solution is to use darker wallpapers and themes. While we've known for a while that lowering the brightness on your devices extends the battery life, it's nice to know just how much it can save you over time. Head over to Wired for the full breakdown and mathematics of it all.